Re: [PATCH] [v2] drm/imx: imx-ldb: fix out of bounds array access warning

[Joe Perches <joe@perches.com>]

On Wed, 2021-03-24 at 13:17 +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> When CONFIG_OF is disabled, building with 'make W=1' produces warnings
> about out of bounds array access:
> 
> drivers/gpu/drm/imx/imx-ldb.c: In function 'imx_ldb_set_clock.constprop':
> drivers/gpu/drm/imx/imx-ldb.c:186:8: error: array subscript -22 is below array bounds of 'struct clk *[4]' [-Werror=array-bounds]
> 
> Add an error check before the index is used, which helps with the
> warning, as well as any possible other error condition that may be
> triggered at runtime.
> 
> The warning could be fixed by adding a Kconfig depedency on CONFIG_OF,
> but Liu Ying points out that the driver may hit the out-of-bounds
> problem at runtime anyway.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> v2: fix subject line
>     expand patch description
>     print mux number
>     check upper bound as well
[]
> diff --git a/drivers/gpu/drm/imx/imx-ldb.c b/drivers/gpu/drm/imx/imx-ldb.c
[]
> @@ -197,6 +197,12 @@ static void imx_ldb_encoder_enable(struct drm_encoder *encoder)
>  	int dual = ldb->ldb_ctrl & LDB_SPLIT_MODE_EN;
>  	int mux = drm_of_encoder_active_port_id(imx_ldb_ch->child, encoder);
> 
> +	if (mux < 0 || mux >= ARRAY_SIZE(ldb->clk_sel)) {
> +		dev_warn(ldb->dev, "%s: invalid mux %d\n",
> +			 __func__, ERR_PTR(mux));

This does not compile without warnings.

drivers/gpu/drm/imx/imx-ldb.c: In function ‘imx_ldb_encoder_enable’:
drivers/gpu/drm/imx/imx-ldb.c:201:22: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘void *’ [-Wformat=]
  201 |   dev_warn(ldb->dev, "%s: invalid mux %d\n",
      |                      ^~~~~~~~~~~~~~~~~~~~~~

If you want to use ERR_PTR, the %d should be %pe as ERR_PTR
is converting an int a void * to decode the error type and
emit it as a string.